1. Field of the Invention
The present invention relates to a lead frame and a method of manufacturing the same and a semiconductor device and, more particularly, a lead frame to which a common wiring portion such as a ground ring, or the like is provided around a die pad and a method of manufacturing the same and a semiconductor device using the lead frame.
2. Description of the Related Art
In the prior art, in some plastic package using the lead frame, the common wiring portion connected to the die pad for the purpose of grounding, or the like is provided like a ring around the die pad onto which the semiconductor chip is mounted.
In such lead frame manufacturing method, as shown in FIG. 1, first, a pattern-shaped metal plate 200a is prepared. In this pattern-shaped metal plate 200a, a ground ring 120 is arranged around a quadrangular die pad 100 and inner leads 140 connected to the ground ring 120 are formed on the outside of the ground ring 120 to extend outward. Outer leads (not shown) connected to the inner leads 140 via a dam bar (not shown) are formed on the outside of the inner leads 140. A support bar 160 extended from an outer frame (not shown) is connected to four corners of the die pad 100 and the ground ring 120 respectively, and the die pad 100 and the ground ring 120 are supported by the support bars 160.
Then, a metal plating layer (not shown) for the wire bonding is formed selectively on the ground ring 120 and the inner leads 140 of the pattern-shaped metal plate 200a. In the lead frame having the ground ring, the ground ring 120 and the inner leads 140 are separated finally. In this case, not to produce defects such as a deformation of the inner leads 140 in the plating step applied to form the metal plating layer, the plating process is carried out in a state that the inner leads 140 are fixed to be connected to the ground ring 120.
Then, as shown in FIG. 2, a die having a supporting member 300, a pressing member 320, and a punch 340 is prepared, and then the pattern-shaped metal plate 200a of FIG. 1 is placed in the die. Then, root portions B of the inner leads 140 connected to the ground ring 120 are pushed and punched by the punch 340 in a state that the ground ring 120 and the inner leads 140 are put between the supporting member 300 and the pressing member 320 to apply a pressure. Thus, as shown in FIG. 3, all the inner leads 140 are cut off from four sides of the ground ring 120 of the pattern-shaped metal plate 200a of FIG. 1. Accordingly, a lead frame 200 having the ground ring 120 can be obtained.
Then, a semiconductor chip (not shown) is mounted on the die pad 100 of the lead frame 200 in FIG. 3, then the semiconductor chip is electrically connected to the ground ring 120 and the inner leads 140 by the wire bonding respectively, and then the semiconductor chip is sealed with a resin. The lead frame 200 is cut off from the outer frame at a predetermined timing, and the bending is applied to the lead frame 200.
The technology associated with the lead frame having the ground ring is set forth in Patent Literature 1 (Patent Application Publication (KOKAI) Hei 6-252328) and Patent Literature 2 (Patent Application Publication (KOKAI) Hei 8-125094), for example.
Also, in Patent Literature 3 (Patent Application Publication (KOKAI) 2000-31370), it is set forth that the, in forming a slope in the stage support bar connected to the stage portion of the lead frame, upper and lower surfaces of the bar are held by a holding means respectively and the holding means are moved relatively in the direction perpendicular to the lead forming surface, so that a slope piece portion stretched uniformly by the stretching is formed.
In the above lead frame manufacturing method in the prior art, when the inner leads 140 are cut off from the ground ring 120 by the die, the problems exist as follows. As shown in FIG. 4A, in the case that the ground ring 120 is pressed tightly by the pressing member 320, the inner leads 140 can be cut off satisfactorily without occurring of a twist due to an inclination of the ground ring 120, nevertheless a surface (metal plating layer) of the ground ring 120 is easily scratched by the pressing member 320 and the supporting member 300. Thus, reliability in connecting the semiconductor chip and the ground ring 120 by the wire bonding is lowered.
Conversely, as shown in FIG. 4B, in the case that the ground ring 120 is pressed loosely by the pressing member 320, generation of the scratch on the surface of the ground ring 120 can be improved, nevertheless a twist is easily caused because the ground ring 120 is inclined. Thus, reliability in executing the wire bonding is lowered similarly.